Manganese- and Platinum-Driven Oxidative and Nitrosative Stress in Oxaliplatin-Associated CIPN with Special Reference to Ca4Mn(DPDP)5, MnDPDP and DPDP.

Platinum-containing chemotherapeutic drugs are efficacious in many forms of cancer but are dose-restricted by serious side effects, of which peripheral neuropathy induced by oxidative-nitrosative-stress-mediated chain reactions is most disturbing. Recently, hope has been raised regarding the catalytic antioxidants mangafodipir (MnDPDP) and calmangafodipir [Ca4Mn(DPDP)5; PledOx®], which by mimicking mitochondrial manganese superoxide dismutase (MnSOD) may be expected to overcome oxaliplatin-associated chemotherapy-induced peripheral neuropathy (CIPN). Unfortunately, two recent phase III studies (POLAR A and M trials) applying Ca4Mn(DPDP)5 in colorectal cancer (CRC) patients receiving multiple cycles of FOLFOX6 (5-FU + oxaliplatin) failed to demonstrate efficacy. Instead of an anticipated 50% reduction in the incidence of CIPN in patients co-treated with Ca4Mn(DPDP)5, a statistically significant increase of about 50% was seen. The current article deals with confusing differences between early and positive findings with MnDPDP in comparison to the recent findings with Ca4Mn(DPDP)5. The POLAR failure may also reveal important mechanisms behind oxaliplatin-associated CIPN itself. Thus, exacerbated neurotoxicity in patients receiving Ca4Mn(DPDP)5 may be explained by redox interactions between Pt2+ and Mn2+ and subtle oxidative-nitrosative chain reactions. In peripheral sensory nerves, Pt2+ presumably leads to oxidation of the Mn2+ from Ca4Mn(DPDP)5 as well as from Mn2+ in MnSOD and other endogenous sources. Thereafter, Mn3+ may be oxidized by peroxynitrite (ONOO-) into Mn4+, which drives site-specific nitration of tyrosine (Tyr) 34 in the MnSOD enzyme. Conformational changes of MnSOD then lead to the closure of the superoxide (O2•-) access channel. A similar metal-driven nitration of Tyr74 in cytochrome c will cause an irreversible disruption of electron transport. Altogether, these events may uncover important steps in the mechanism behind Pt2+-associated CIPN. There is little doubt that the efficacy of MnDPDP and its therapeutic improved counterpart Ca4Mn(DPDP)5 mainly depends on their MnSOD-mimetic activity when it comes to their potential use as rescue medicines during, e.g., acute myocardial infarction. However, pharmacokinetic considerations suggest that the efficacy of MnDPDP on Pt2+-associated neurotoxicity depends on another action of this drug. Electron paramagnetic resonance (EPR) studies have demonstrated that Pt2+ outcompetes Mn2+ and endogenous Zn2+ in binding to fodipir (DPDP), hence suggesting that the previously reported protective efficacy of MnDPDP against CIPN is a result of chelation and elimination of Pt2+ by DPDP, which in turn suggests that Mn2+ is unnecessary for efficacy when it comes to oxaliplatin-associated CIPN.

Exacerbated Neuropathy in POLAR A and M Trials Due to Redox Interaction of PledOx-Associated Mn2+ and Oxaliplatin-Associated Pt2.

Disappointing results from the POLAR A and M phase III trials involving colorectal cancer patients on chemotherapy with FOLFOX6 in curative (A) and palliative (M) settings have been reported by the principal investigators and the sponsor (PledPharma AB/Egetis Therapeutics AB). FOLFOX6, oxaliplatin in combination with 5-fluorouracil (5-FU), possesses superior tumoricidal activity in comparison to 5-FU alone, but suffers seriously from dose-limiting platinum-associated Chemotherapy-Induced Peripheral Neuropathy (CIPN). The aim of the POLAR trials was to demonstrate that PledOx [calmangafodipir; Ca4Mn(DPDP)5] reduced the incidence of persistent CIPN from 40% to 20%. However, this assumption was based on "explorative" data in the preceding PLIANT phase II trial, which did not mirror the expected incidence of unwanted toxicity in placebo patients. In POLAR A and M, the assessment of PledOx efficacy was conducted in patients that received at least six cycles of FOLFOX6, enabling analyses of efficacy in 239 A and 88 M patients. Instead of a hypothesized improvement from 40% to 20% incidence of persistent CIPN in the PledOx group, i.e., a 50% improvement, the real outcome was the opposite, i.e., an about 50% worsening in this bothersome toxicity. Mechanisms that may explain the disastrous outcome, with a statistically significant number of patients being seriously injured after having received PledOx, indicate interactions between two redox active metal cations, Pt2+ (oxaliplatin) and Mn2+ (PledOx). A far from surprising causal relationship that escaped prior detection by the study group and the sponsor. Most importantly, recently published data (ref 1) unequivocally indicate that the PLIANT study was not suited to base clinical phase III studies on. In conclusion, the POLAR and PLIANT trials show that PledOx and related manganese-containing compounds are unsuited for co-treatment with platinum-containing compounds. For use as a therapeutic adjunct in rescue treatment, like in ischemia-reperfusion of the heart or other organs, or in acetaminophen (paracetamol)-associated liver failure, there is little or nothing speaking against the use of PledOx or other PLED compounds. However, this must be thoroughly documented in more carefully designed clinical trials.

The Damaging Outcome of the POLAR Phase III Trials Was Due to Avoidable Time-Dependent Redox Interaction between Oxaliplatin and PledOx.

On 2 July 2021, highly negative results were reported from the POLAR A and M phase III trials in patients with colorectal cancer, treated with an oxaliplatin-based regimen and co-treated with calmangafodipir (CaM; PledOx®; PledPharma AB/Egetis Therapeutics AB) or placebo. The results revealed persistent chemotherapy-induced peripheral neuropathy (CIPN) in 54.8% of the patients treated with PledOx, compared with 40.0% of the patients treated with the placebo (p < 0.05), i.e., a 37% increase in incidence of the side effect that the trial was aimed to prevent. The damaging outcome of the trials differed diametrically from an in-parallel conducted mice study and from a clinical trial with mangafodipir, the active ingredient of CaM. According to the authors of the POLAR report, the etiology of the profound increase in CIPN in the PledOx arm is unclear. However, these devastating effects are presumably explained by intravenous administrations of PledOx and oxaliplatin being too close in time and, thereby, causing unfavorable redox interactions between Mn2+ and Pt2-. In the mice study as well as in the preceding phase II clinical trial (PLIANT), PledOx was administered 10 min before the start of the oxaliplatin infusion; this was clearly an administration procedure, where the devastating interactions between PledOx and oxaliplatin could be avoided. However, when it comes to the POLAR trials, PledOx was administered, for incomprehensible reasons, "on Top of Modified FOLFOX6" at day one, i.e., after the two-hour oxaliplatin infusion instead of before oxaliplatin. This is a time point when the plasma concentration of oxaliplatin and Pt2+-metabolites is at its highest, and where the risk of devastating redox interactions between PledOx and oxaliplatin, in turn, is at its highest.

May Mangafodipir or Other SOD Mimetics Contribute to Better Care in COVID-19 Patients?

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is characterized by massive inflammation of the arterial endothelium accompanied by vasoconstriction and widespread pulmonary micro thrombi. As a result, due to the destruction of nitric oxide (•NO) by inflammatory superoxide (O2•-), pulmonary •NO concentration ceases, resulting in uncontrolled platelet aggregation and massive thrombosis, which kills the patients. Introducing •NO by inhalation (INO) may replace the loss of endothelium-derived •NO. The first results from clinical trials with INO in SARS-CoV-2 patients show a rapid and sustained improvement in cardiopulmonary function and decreased inflammation. An ongoing phase III study is expected to confirm the method's efficacy. INO may hence become a first line treatment in SARS-CoV-2 patients. However, due to the rapid inactivation of •NO by deoxyhemoglobin to nitrate, pulmonary administration of •NO will not protect remote organs. Another INO-related pharmacological approach to protect SARS-CoV-2 patients from developing life-threatening disease is to inhibit the O2•--driven destruction of •NO by neutralizing inflammatory O2•-. By making use of low molecular weight compounds that mimic the action of the enzyme manganese superoxide dismutase (MnSOD). The MnSOD mimetics of the so-called porphyrin type (e.g., AEOL 10150), salen type (e.g., EUK-8) and cyclic polyamine type (e.g., M40419, today known as GC4419 and avasopasem manganese) have all been shown to positively affect the inflammatory response in lung epithelial cells in preclinical models of chronic obstructive pulmonary disease. The Manganese diPyridoxyL EthylDiamine (MnPLED)-type mangafodipir (manganese dipyridoxyl diphosphate-MnDPDP), a magnetic resonance imaging (MRI) contrast agent that possesses MnSOD mimetic activity, has shown promising results in various forms of inflammation, in preclinical as well as clinical settings. Intravenously administration of mangafodipir will, in contrast to INO, reach remote organs and may hence become an important supplement to INO. From the authors' viewpoint, it appears logical to test mangafodipr in COVID-19 patients at risk of developing life-threatening SARS-CoV-2. Five days after submission of the current manuscript, Galera Pharmaceuticals Inc. announced the dosing of the first patient in a randomized, double-blind pilot phase II clinical trial with GC4419 for COVID-19. The study was first posted on ClinicalTrials.gov (Identifier: NCT04555096) 18 September 2020.

Comment on "Calmangafodipir Reduces Sensory Alterations and Prevents Intraepidermal Nerve Fibers Loss in a Mouse Model of Oxaliplatin Induced Peripheral Neurotoxicity" Antioxidants 2020, 9, 594.

We have with enthusiasm read the article "Calmangafodipir Reduces Sensory Alterations and Prevents Intraepidermal Nerve Fibers Loss in a Mouse Model of Oxaliplatin Induced Peripheral Neurotoxicity"[...].

Evidence that fodipir (DPDP) binds neurotoxic Pt2+ with a high affinity: An electron paramagnetic resonance study.

Oxaliplatin typically causes acute neuropathic problems, which may, in a dose-dependent manner, develop into a chronic form of chemotherapy-induced peripheral neuropathy (CIPN), which is associated with retention of Pt2+ in the dorsal root ganglion. A clinical study by Coriat and co-workers suggests that co-treatment with mangafodipir [Manganese(II) DiPyridoxyl DiPhosphate; MnDPDP] cures ongoing CIPN. These authors anticipated that it is the manganese superoxide dismutase mimetic activity of MnDPDP that explains its curative activity. However, this is questionable from a pharmacokinetic perspective. Another, but until recently undisclosed possibility is that Pt2+ outcompetes Mn2+/Ca2+/Zn2+ for binding to DPDP or its dephosphorylated metabolite PLED (diPyridoxyL EthylDiamine) and transforms toxic Pt2+ into a non-toxic complex, which can be readily excreted from the body. We have used electron paramagnetic resonance guided competition experiments between MnDPDP (10logKML ≈ 15) and K2PtCl4, and between MnDPDP and ZnCl2 (10logKML ≈ 19), respectively, in order to obtain an estimate the 10logKML of PtDPDP. Optical absorption spectroscopy revealed a unique absorption line at 255 nm for PtDPDP. The experimental data suggest that PtDPDP has a higher formation constant than that of ZnDPDP, i.e., higher than 19. The present results suggest that DPDP/PLED has a high enough affinity for Pt2+ acting as an efficacious drug in chronic Pt2+-associated CIPN.

Mangafodipir a Selective Cytoprotectant - with Special Reference to Oxaliplatin and Its Association to Chemotherapy-Induced Peripheral Neuropathy (CIPN).

Oxaliplatin, in combination with 5-fluorouracil plus folinate (or capecitabine), has increased survival substantially in stage III colorectal cancer and prolonged life in stage IV patients, but its use is compromised because of severe toxicity. Chemotherapy-induced peripheral neuropathy (CIPN) is the most problematic dose-limiting toxicity of oxaliplatin. Oncologists included for years calcium and magnesium infusion as part of clinical practice for preventing CIPN. Results from a phase III prospective study published in 2014, however, overturned this practice. No other treatments have been clinically proven to prevent this toxicity. There is a body of evidence that CIPN is caused by cellular oxidative stress. Clinical and preclinical data suggest that the manganese chelate and superoxide dismutase mimetic mangafodipir (MnDPDP) is an efficacious inhibitor of CIPN and other conditions caused by cellular oxidative stress, without interfering negatively with the tumoricidal activity of chemotherapy. MnPLED, the metabolite of MnDPDP, attacks cellular oxidative stress at several critical levels. Firstly, MnPLED catalyzes dismutation of superoxide (O2•-), and secondly, having a tremendous high affinity for iron (and copper), PLED binds and disarms redox active iron/copper, which is involved in several detrimental oxidative steps. A case report from 2009 and a recent feasibility study suggest that MnDPDP may prevent or even cure oxaliplatin-induced CIPN. Preliminary results from a phase II study (PLIANT) suggest efficacy also of calmangafodipir, but these results are according to available data obscured by a surprisingly low number of adverse events and a seemingly lower than expected efficacy of FOLFOX.

Calmangafodipir [Ca4Mn(DPDP)5], mangafodipir (MnDPDP) and MnPLED with special reference to their SOD mimetic and therapeutic properties.

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) participate in pathological tissue damage. Mitochondrial manganese superoxide dismutase (MnSOD) normally keeps ROS and RNS in check. During development of mangafodipir (MnDPDP) as a magnetic resonance imaging (MRI) contrast agent, it was discovered that MnDPDP and its metabolite manganese pyridoxyl ethyldiamine (MnPLED) possessed SOD mimetic activity. MnDPDP has been tested as a chemotherapy adjunct in cancer patients and as an adjunct to percutaneous coronary intervention in patients with myocardial infarctions, with promising results. Whereas MRI contrast depends on release of Mn(2+), the SOD mimetic activity depends on Mn(2+) that remains bound to DPDP or PLED. Calmangafodipir [Ca4Mn(DPDP)5] is stabilized with respect to Mn(2+) and has superior therapeutic activity. Ca4Mn(DPDP)5 is presently being explored as a chemotherapy adjunct in a clinical multicenter Phase II study in patients with metastatic colorectal cancer.

Effects of MnDPDP and ICRF-187 on Doxorubicin-Induced Cardiotoxicity and Anticancer Activity.

Oxidative stress participates in doxorubicin (Dx)-induced cardiotoxicity. The metal complex MnDPDP and its metabolite MnPLED possess SOD-mimetic activity, DPDP and PLED have, in addition, high affinity for iron. Mice were injected intravenously with MnDPDP, DPDP, or dexrazoxane (ICRF-187). Thirty minutes later, mice were killed, the left atria were hung in organ baths and electrically stimulated, saline or Dx was added, and the contractility was measured for 60 minutes. In parallel experiments, 10 µM MnDPDP or MnPLED was added directly into the organ bath. The effect of MnDPDP on antitumor activity of Dx against two human tumor xenografts (MX-1 and A2780) was investigated. The in vitro cytotoxic activity was studied by co-incubating A2780 cells with MnDPDP, DPDP, and/or Dx. Dx caused a marked reduction in contractile force. In vivo treatment with MnDPDP and ICRF-187 attenuated the negative effect of Dx. When added directly into the bath, MnDPDP did not protect, whereas MnPLED attenuated the Dx effect by approximately 50%. MnDPDP or ICRF-187 did not interfere negatively with the anti-tumor activity of Dx, either in vivo or in vitro. Micromolar concentrations of DPDP but not MnDPDP displayed an in vitro cytotoxic activity against A2780 cells. The present results show that MnDPDP, after being metabolized to MnPLED, protects against acute Dx cardiotoxicity. Both in vivo and in vitro experiments show that cardioprotection takes place without interfering negatively with the anticancer activity of Dx. Furthermore, the results suggest that the previously described cytotoxic in vivo activity of MnDPDP is an inherent property of DPDP.

First clinical experience with the magnetic resonance imaging contrast agent and superoxide dismutase mimetic mangafodipir as an adjunct in cancer chemotherapy-a translational study.

Preclinical research suggests that the clinically approved magnetic resonance imaging contrast agent mangafodipir may protect against adverse events (AEs) caused by chemotherapy, without interfering negatively with the anticancer efficacy. The present translational study tested if pretreatment with mangafodipir lowers AEs during curative (adjuvant) FOLFOX6 chemotherapy in stage III colon cancer (Dukes' C). The study was originally scheduled to include 20 patients, but because of the unforeseen withdrawal of mangafodipir from the market, the study had to be closed after 14 patients had been included. The withdrawal of mangafodipir was purely based on commercial considerations from the producer and not on any safety concerns. The patients were treated throughout the first 3 of 12 scheduled cycles. Patients were randomized to a 5-minute infusion of either mangafodipir or placebo (7 in each group). AEs were evaluated according to the National Cancer Institute's (NCI) Common Terminology Criteria for Adverse Events and the Sanofi-NCI criteria. The primary end points were neutropenia and neurosensory toxicity. There were four AEs of grade 3 (severe) and one AE of grade 4 (life threatening) in four patients in the placebo group, whereas there were none in the mangafodipir group (P < .05). Of the grade 3 and 4 events, two were neutropenia and one was neurosensory toxicity. Furthermore, white blood cell count was statistically, significantly higher in the mangafodipir group than in the placebo group (P < .01) after treatment with FOLFOX. This small feasibility study seems to confirm what has been demonstrated preclinically, namely, that pretreatment with mangafodipir lowers AEs during adjuvant 5-fluorouracil plus oxaliplatin-based chemotherapy in colon cancer patients.

Superior therapeutic index of calmangafodipir in comparison to mangafodipir as a chemotherapy adjunct.

Mangafodipir is a magnetic resonance imaging contrast agent with manganese superoxide dismutase (MnSOD) mimetic activity. The MnSOD mimetic activity protects healthy cells against oxidative stress-induced detrimental effects, e.g., myelosuppressive effects of chemotherapy drugs. The contrast property depends on in vivo dissociation of Mn(2+) from mangafodipir-about 80% dissociates after injection. The SOD mimetic activity, however, depends on the intact Mn complex. Complexed Mn(2+) is readily excreted in the urine, whereas dissociated Mn(2+) is excreted slowly via the biliary route. Mn is an essential but also a potentially neurotoxic metal. For more frequent therapeutic use, neurotoxicity due to Mn accumulation in the brain may represent a serious problem. Replacement of 4/5 of Mn(2+) in mangafodipir with Ca(2+) (resulting in calmangafodipir) stabilizes it from releasing Mn(2+) after administration, which roughly doubles renal excretion of Mn. A considerable part of Mn(2+) release from mangafodipir is governed by the presence of a limited amount of plasma zinc (Zn(2+)). Zn(2+) has roughly 10(3) and 10(9) times higher affinity than Mn(2+) and Ca(2+), respectively, for fodipir. Replacement of 80% of Mn(2+) with Ca(2+) is enough for binding a considerable amount of the readily available plasma Zn(2+), resulting in considerably less Mn(2+) release and retention in the brain and other organs. At equivalent Mn(2+) doses, calmangafodipir was significantly more efficacious than mangafodipir to protect BALB/c mice against myelosuppressive effects of the chemotherapy drug oxaliplatin. Calmangafodipir did not interfere negatively with the antitumor activity of oxaliplatin in CT26 tumor-bearing syngenic BALB/c mice, contrary calmangafodipir increased the antitumor activity.

Contrast enhancement of manganese-hydroxypropyl-tetraacetic acid, an MR contrast agent with potential for detecting differences in myocardial blood flow.

PURPOSE: To determine whether the contrast agent MnHPTA has potential for detecting differences in myocardial blood flow. MATERIALS AND METHODS: R1 in the myocardium was calculated from MR signal intensity measurements in 18 pigs after intravenous injection of 5, 15, or 25 micromol MnHPTA/kg body weight. Measurements were made in each animal after administration at rest and during dobutamine-induced stress. RESULTS: A difference of approximately 0.1 sec-1 in the R1 increase between rest and stress still remained 31 minutes after administration of 25 micromol MnHPTA/kg body weight. When two consecutive MnHPTA injections were performed, the second injection induced a lower R1 increase than the corresponding first injection. CONCLUSION: MnHPTA at a dose of 25 micromol/kg body weight (b.w.) has the potential to detect perfusion differences in myocardium. When two consecutive injections of MnHPTA were administered, the R1 change after the second injection was affected by the earlier administration. Therefore, a protocol including more than one administration is not ideal for this contrast agent.

Acetylcholine-induced vasodilation may depend entirely upon NO in the femoral artery of young piglets.

1 To characterize agonist-induced relaxation in femoral artery rings from young piglets, we compared the effect of a NOS-inhibitor N(omega)-nitro-L-arginine (L-NOARG), an NO-inactivator oxyhaemoglobin (HbO) and a soluble guanyl cyclase(sGC)-inhibitor 1H-[1,2,4]Oxadiazolo-[4,3,-alpha]quinoxalin-1-one (ODQ) on acetylcholine(ACh)-induced relaxation. The involvement of K(+) channel activation was studied on relaxations induced by ACh, the two NO donors sodium nitroprusside (SNP) and diethylamine (DEA) NONOate, and the cell membrane permeable guanosine 3'5' cyclic monophosphate (cGMP) analogue 8-Br-cGMP. 2 Full reversal of phenylephrine-mediated precontraction was induced by ACh (1 nM-1 microM) (pD(2) 8.2+/-0.01 and R(max) 98.7+/-0.3%). L-NOARG (100 microM) partly inhibited relaxation (pD(2) 7.4+/-0.02 and R(max) 49.6+/-0.8%). The L-NOARG/indomethacin(IM)-resistant response displayed characteristics typical for endothelium-derived hyperpolarizing factor (EDHF), being sensitive to a combination of the K(+) channel blockers charybdotoxin (CTX) (0.1 microM) and apamin (0.3 microM). 3 ODQ (10 microM) abolished relaxations induced by ACh and SNP. L-NOARG/IM-resistant relaxations to ACh were abolished by HbO (20 microM). 4 Ouabain (1 microM) significantly inhibited ACh-induced L-NOARG/IM-resistant relaxations and relaxations induced by SNP (10 microM) and 8-Br-cGMP (0.1 mM). A combination of ouabain and Ba(2+) (30 microM) almost abolished L-NOARG/IM-resistant ACh-induced relaxation (R(max) 7.7+/-2.5% vs 23.4+/-6.4%, with and without Ba(2+), respectively, P<0.05). 5 The present study demonstrates that in femoral artery rings from young piglets, despite an L-NOARG/IM-resistant component sensitive to K(+) channel blockade with CTX and apamin, ACh-induced relaxation is abolished by sGC-inhibition or a combination of L-NOARG and HbO. These findings suggest that relaxation can be fully explained by the NO/cGMP pathway.